$f(x) = \begin{cases} -4 & \text{if } x = -1 \\ -x^{2}-1 & \text{otherwise} \end{cases}$ What is the range of $f(x)$ ?
First consider the behavior for $x \ne -1$ Consider the range of $-x^{2}$ The range of $x^2$ is $\{\, y \mid y \ge 0 \,\}$ Multiplying by $-1$ flips the range to $\{\, y \mid y \le 0 \,\}$ To get $-x^{2}-1$ , we subtract $1$ So the range becomes: $\{\, y \mid y ≤ -1 \,\}$ If $x = -1$, then $f(x) = -4$. Since $-4 ≤ -1$, the range is still $\{\, y \mid y ≤ -1 \,\}$.